In the prior art structural units of the autobuses, parts of the drive, such as the clutch and transmission, gear box and the auxiliary devices, such as the generator, air-filter, compressor, silencer, are mounted generally independently from the frame. These elements are generally attached to the main frame through accessory racks mounted into the frame structure, through holding devices, or by inserting some elastic element, such as a rack made of rubber.
A drawback of such traditional arrangements and modes of attachment is that reactive moments arising during the operation of the motor vehicle, a direct and considerable load is exerted on the vehicle frame. Depending on the load extraordinary local stresses may occur in the vehicle frame. These are partly large local stresses, and further, the constantly changing dynamic loading, and the generally symmetrical arrangement of the frame structure about the longitudinal axis of the vehicle, together lead, according to practical experience, to localized peak stresses, which negatively influence the useful life of autobuses.
The frame structure has to be excessively reinforced to eliminate local stresses, and this requires the undue expenditure of material, weight and other costs.
In addition to the aforementioned disadvantages, the above added reinforced mode by the prior art does not meet modern assembly or maintenance requirements while it is also complex, time consuming, and costly.
Hungarian patent No. 183,364 describes a mounting frame carrying the vehicle engine which can be connected to the understructure of the motor vehicle in a releasable way. This enables pre-assembled suspension of the engine and optionally the gear box assembled therewith. This frame is connected at four points to the understructure by supporting brackets by using horizontal clamping screws disposed in sleeves. The frame is a structure welded from longitudinal and transverse beams, and the engine is mounted on the supporting brackets of the frame.
Although the rearward extending frame enables a certain amount of pre-assembly, and enables installation of various types of engines or frames supporting various transmissions to the understructure of the same vehicle, also in this case, one has to consider that result of symmetrical arrangement and support whereby reactive moments due to drive and mass forces can lead to undesired local stress peaks which are indirectly transferred to the frame and bring about the aforementioned disadvantages. The problem is increased by the subsequent installation and arrangement of auxiliary devices having considerable mass.